class Solution
{
    int dx[4] = { 1,-1,0,0 };
    int dy[4] = { 0,0,1,-1 };
    int ret;
    vector<vector<bool>>vis;
    int m, n;
public:
    int numIslands(vector<vector<char>>& grid)
    {
        m = grid.size();
        n = grid[0].size();
        vis = vector<vector<bool>>(m, vector<bool>(n));
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (!vis[i][j] && grid[i][j] == '1')
                {
                    ret++;
                    dfs(grid, i, j);
                }
            }
        }
        return ret;
    }

    void dfs(vector<vector<char>>& grid, int i, int j)
    {
        vis[i][j] = true;
        for (int k = 0; k < 4; k++)
        {
            int x = dx[k] + i;
            int y = dy[k] + j;
            if (x >= 0 && x < m && y >= 0 && y < n && vis[x][y] == false && grid[x][y] == '1')
            {
                dfs(grid, x, y);
            }
        }
    }
};